Late this afternoon through Sunday a broad surface low stretching
from Quebec to Maine will consolidate and drift east into the Gulf
of Saint Lawrence. An area of deep wrap around moisture will cross
the eastern Great Lakes tonight and Sunday morning, while ongoing
cold advection cools the column. Deep saturation and low level flow
normal to the Chautauqua Ridge will produce a near ideal setup for
strong upslope enhancement across the higher terrain east of Lake
Erie. Forecast soundings show a deep 5-7K foot thick dendritic
growth zone tonight through Sunday morning. The airmass will grow
cold enough for lake enhancement as well from late tonight through
Sunday. The same will occur east of Lake Ontario across the Tug
Hill, although flow will veer more WNW by Sunday, with less
favorable lake enhancement following the initial development
tonight. Outside of the main upslope areas east of the lakes, expect
periods of snow tonight through Sunday and possibly a few meandering
bands of Lake Huron and Georgian Bay lake effect to produce minor
accumulations.
As far as accumulations go, the 00Z high-res guidance that handles
smaller scale upslope better than global guidance, continued an
upward trend, and this raises the chances of warning criteria being
reached for the higher terrain east of Lake Erie. Expect total
accumulations in the 8-14" range along a narrow zone of the
Chautauqua Ridge from Sherman to Perrysburg, and 7-12" across the
Boston Hills and the ridges of western Wyoming County. There will be
far less snow along the Lake Erie shore (including the Thruway), and
steadily decreasing snow inland from the Chautauqua Ridge. East of
Lake Ontario, expect 6-10" across the Tug Hill tonight through
Sunday. The setup is not quite as favorable here, so we have opted
for a higher end Advisory for the Tug Hill, although a small area of
warning criteria snow is possible near the Oswego/Jefferson/Lewis
County triple point. Outside of these two areas, expect
accumulations of 2-4" tonight through Sunday in most areas. The one
caveat, if a Lake Huron band were to stall over the Niagara Frontier
or south of Lake Ontario higher amounts are possible.